Research:

We study the dynamics of chemical reactions. In particular, we are interested in studying events involving highly excited molecules with a chemically significant amount of energy. Highly excited molecules are of great importance, due to their reactivity; however, they are often extremely difficult to study as a result of their complexity. Reactants are produced using laser pumping techniques after which we observe the outcome of either a bimolecular collisional energy transfer event, or a unimolecular or bimolecular reaction.

The goal of our studies is to understand these chemically significant events in a quantum state resolved fashion with detail that was, until recently, only dreamed of. We use novel high resolution spectroscopic techniques (~0.0003 cm-1) to study the amount of energy distributed in the various energy states (vibration, rotation, and translation) of molecules after a reaction or collision. Current projects can be divided into three general classes:

Collisional Energy Transfer is one of the key steps in the Lindemann mechanism for unimolecular reactions. Collisional deactivation competes with chemical reaction by removing enough energy to bring the reactant species below threshold. By studying the final rotational and vibrational quantum states as well as the translational energy distributions of simple collision partners, we can establish the probability of transferring a specific amount and type of energy. The results from this quantum state picture can be converted into a probability distribution function, which provides information about the transition state and potential energy surface of the interaction.

Photo-Induced Chemical Reaction Dynamics and Kinetics. Using similar techniques, it is possible to track the products of a photodissociation process with quantum state resolution. Because the molecules used to study collisional energy transfer have such a large amount of energy (~5 eV), they are literally ready to explode into molecular and atomic fragments when the collision event takes place. Unimolecular decomposition is thus in competition with collisional energy transfer. By probing the molecular fragments, it is possible to follow the course of these photo-induced chemical reactions with detail never before observed. It is possible to extract not only the reaction rate, but also learn a great deal about fundamental properties of chemical reactions.

Combustion Chemistry. The combustion of methane is of considerable importance in the generation of energy; thus, it has received considerable attention. This apparently simple chemical reaction is actually not so simple. The kinetics of the reaction of methyl radicals with oxygen atoms, the key step in the overall combustion process, has been studied extensively; however, a consensus has yet to be reached in our understanding of this important reaction. Some of the controversy is potentially tied to methyl radical production. Understanding the photodissociation dynamics of methyl radical precursors, particularly the partitioning of energy among the various quantum states, is of utmost importance if a completely clear picture is to be obtained for the reaction of CH3 with O(3P). It is highly improbable that various methods of CH3 production produce radicals with the same characteristics; thus, the outcome of subsequent reactions will also, most likely, be different. In addition to performing a detailed quantum state resolved study of methyl radical formation, we are also interested in studying the subsequent chemical reactions. We hope the clues uncovered will increase the understanding of this reaction, in specific, and other chemical systems, generally.